Scientists around the world often work on similar data so the need to share results and compare data arises periodically. We describe a method of comparing image of two similar samples created in different laboratories to help identify or suggest protein spot identification. Now that 2D gels and associated databases (DB) frequently appear on the Internet, this opens up the possibility of visually comparing one's own experimental 2D gel image data with data from another gel in a remote Internet DB. In general, there are a few ways to compare images: 1) slide one autoradiograph or stained gel over the other while back- illuminated; or 2) build a 2D gel computer DB from both gels after scanning and analyzing these gels. These are impractical since in the former case, the gel from the Internet DB is not locally available, while the costs of building a full DB is excessive if only a single visual comparison is needed. We describe a distributed gel comparison program (URL:http://www-lecb.ncifcrf.gov/flicker) which runs on any Web browser and is invoked by clicking on a request from the web browser. One image is read from any Internet 2D gel DB (eg.SWISS-2DPAGE) and the other from the investigator's computer. Images may be more easily compared by first applying spatial warping or other transforms. As the two possibly transformed images are rapidly alternated, or flickered, in the same window, the user can slide one image past the other to visually align corresponding spots or regions by matching local morphology. This flicker-comparison technique may be applied to analyzing other types of 1D and 2D biomedical images. We have developed a 2DWG meta-database of 2D gel images found on the Web and integrated it with Flicker to make it easier to compare images (http:www- lecb.ncifcrf.gov/2dwgDB/).